An LCD (Liquid crystal display) device with a touch screen display integrated thereinto has been widely applied as, for example, the display for portable notebook computer, and the input device for cellular phone, electric household appliances, public information systems, office automated apparatus, etc.
A conventional touch screen display mainly includes a glass substrate being coated on one surface with a layer of transparent conductive layer, such as an indium-tin oxide conductive layer; a thin film being coated on a bottom surface with a transparent conductive layer corresponding to the transparent conductive layer on the glass substrate; and a plurality of insulating dot spacers provided between the transparent conductive layer on the glass substrate and the transparent conductive layer below the thin film for spacing the two transparent layers from each other. When the touch screen display is touched during an operation, a touch signal is generated and transmitted to a controller via a signal line. There is also another type of conventional touch screen display that adopts a capacitive touch sensing structure.
Among different structural designs for conventional LCD devices, there is a thin film transistor (TFT) LCD that mainly includes a glass substrate, a liquid crystal layer, two polarizing plates, a color filter layer, a backlight source, a pixel electrode layer located below the liquid crystal layer, and a common electrode layer located atop the liquid crystal layer. The common electrode layer and the pixel electrode layer together form a liquid crystal driving electrode layer for driving the liquid crystal layer.
Another type of LCD device is referred to as an in-plane switching mode (IPS mode) LCD, which is structurally similar to the TFT LCD, except that it adopts a horizontally arranged liquid crystal driving electrode structure formed between the glass substrate and a bottom surface of the liquid crystal layer. The liquid crystal driving electrode layer includes a plurality of staggered pixel electrodes and common electrodes for driving the liquid crystal layer.
While the integrated touch screen display and LCD device provides high practicability, it has the problem of mutual interference between the touch signal and the liquid crystal driving signal due to a extremely close distance between the touch screen display and the liquid crystal layer, the pixel electrode, and the common electrode of the LCD.
Further, in an analysis on capacitive effect, it is found the interference of capacitive coupling exists between the pixel and common electrodes of the LCD device and a touch sensing layer of the touch screen display. In addition, there is also interference of high-frequency signal between the LCD module and the touch sensing layer. These interferences are noise interferences in terms of the capacitive coupling formed between the touch sensing layer and a part of human body, and would adversely affect the accuracy in detecting the position of a touched point on the touch screen display. Meanwhile, a relatively high driving voltage used to obtain enhanced brilliance further intensifies the problem of noise interference.
The above-mentioned problems of signal interference occur in both the general TFT LCD and the IPS mode LCD.